JP2634953B2 - Method for producing iron / polymer powder composition - Google Patents

Abstract

A powder composition of iron-based powder particles to which is bonded a polymeric material is prepared by making a dry admixture of the iron-based particles and particles of the polymer, wetting the admixture with a solvent for the polymeric material, and removing the solvent to leave a flowable powder composition. The powder compositions can be compression moulded, generally at a temperature above the glass transition temperature of the polymer, to form magnetic core components.

Description

Description: FIELD OF THE INVENTION The present invention relates to a method of making a powder composition comprising iron-based powder particles bonded to a polymeric material in a generally particulate form. More particularly, the method of the present invention relates to the use of a solvent for the polymeric material that first mixes the iron and polymer in dry form, and then causes the polymer to bind to the iron particles. The powder particles thus produced are particularly useful for producing a magnetic core component.

BACKGROUND OF THE INVENTION Iron-substrate particles have long been used as substrates in the manufacture of structural components by powder metallurgy. The desired shape is obtained by molding in a die under high pressure without losing the iron-base particles. After the molding step, the structural component typically undergoes a sintering step to impart the necessary strength to the component.

Magnetic core components have also been produced by such powder metallurgy methods, but the iron-based particles used in these methods are generally coated with a circumferential layer of insulating material.

Two important properties of the iron core component are its permeability and core loss properties. The permeability of a material is an indicator of its ability to magnetize, or of its ability to carry magnetic flux. Permeability is defined as the ratio of the induced magnetic flux to the magnetizing force or field strength. When a magnetic material is exposed to a rapidly changing field, the total energy of the core is
It is reduced by the occurrence of hysteresis loss and / or eddy current loss. Energy loss overcomes the magnetic forces held within the iron core component caused by the necessary consumption of energy. Eddy current losses are caused by the generation of current in the iron core component due to the changing flux caused by changing the current state.

Early magnetic core components were made from laminated sheet steel, but these components were difficult to manufacture and experienced significant core loss at higher frequencies. The application of these laminate-substrate cores is also limited by the need to have a magnetic flux in the plane of the sheet to avoid excessive eddy current losses. Sintered metal powders have been used to replace laminated sheets as a material for the magnetic core component, but these sintered parts also have high core losses and mainly place restrictions on directing current operation. Received.

Research in powder metallurgy manufacturing of magnetic core components using coated iron-substrate powders has been directed to the development of iron powder compositions that enhance certain physical and magnetic properties without adversely affecting other properties. Have been. Desirable properties include high permeability over a wide frequency range, high compressive strength, low core loss, and compatibility with compositional molding techniques.

When molding core components for AC power applications, it is generally required that the iron particles have an electrically insulating coating to reduce core loss. Use of plastic coating on iron particles (U.S. Pat.
5,340) and the use of double-coated iron particles (see U.S. Pat. No. 4,601,765 to Soiler et al.) Were used to insulate the iron particles and thus reduce eddy current losses.

Recently, the following has been found. That is, the insulating polymeric material need not be present in the powder composition as a sufficient coating of the individual iron particles, but rather can be present in discrete particles and the particles are completely mixed with the iron particles. The present invention relates to a method of forming this mixture in such a way as to ensure homogeneity and thereby improve the magnetism of the pressurized part made of the iron composition. The present invention eliminates the need to apply a coating around the polymeric material to the iron-based particles, which generally required the use of a more expensive fluidized bed process.

SUMMARY OF THE INVENTION The present invention provides a method of making an iron / polymer powder composition, the composition comprising iron-based powder particles and a polymeric material bound to the iron-based powder particles. According to this method, a dry mixture of iron-base particles and polymer particles is produced. Generally, the polymeric material will comprise about 0.001 to 15% by weight of the combined weight of iron-based particles and polymer. The dry mixture is then wetted with the polymeric solvent. Preferably, the solvent is sprinkled over the mixture, while the mixture is further mixed. Thereafter, the solvent is removed, leaving a flowable powder composition of iron-substrate particles bound to the polymeric material.

The method is applicable for forming powder compositions from any iron-based particles and polymeric materials. "Iron-
By "substrate particles" is meant to include, but is not limited to, any iron-containing particles commonly used in powder metallurgy processes, including, but not limited to, substantially pure iron and transition metals and / or other metals. Also means pre-alloyed iron particles with the strengthening element. Although this method is applicable to the use of any polymeric material, it has its most significant utility with respect to the use of a magnetic core component. Preferred thermoplastic materials are biphenylene ether and polyetherimide, and the preferred solvent for use with these polymers is methylene chloride.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, the following has been found. That is, the polymeric insulating material can be glued or bonded to the iron-based powder and will provide a magnetic core component having substantially homogeneity and excellent magnetic properties upon compression. A composition is provided. According to the present invention, the iron-substrate particles and the particles of the polymeric material are first mixed, generally in the dry state, to form two substantially homogeneous mixtures. The dry mixture is then contacted with a relatively small amount of solvent for the polymer in a manner to ensure substantial wetting of the entire mixture, as described more fully below. Thereafter, the solvent is removed to provide a dry, free-flowing powder composition of the iron-base particles to which the polymer material is bound. The magnetic core component can then be produced from the powder composition by known methods.

Iron-based particles useful in the present invention are any pure iron or iron-coated (steel or ferromagnetic) particles commonly used in powder metallurgy processes. Examples include substantially pure iron as well as iron pre-alloyed particles with other elements (eg, steel-making elements), where the other elements include strength, hardenability, and electromagnetic properties of the final product. An element that increases a property or other desired property. The particles of the iron-base material useful in the present invention are:
It can have a small weight average particle size of microns or less, or up to about 850 to 1,000 microns, but generally the particles will have a weight average particle size in the range of about 10 to 500 microns. Particle compositions having a maximum average particle size of about 350 microns are preferred, and a maximum average particle size of about 350 microns.
Particle compositions having 250 microns are more preferred.

Preferred iron-based particles for use in the present invention are substantially pure iron highly compressible powders; that is, containing up to about 1.0% by weight, preferably up to about 0.5% by weight of common impurities. It is iron. An example of such a metallurgical grade of pure iron powder is the ANCORSTEEL 1000 series of iron powders available from Höganäs (Riverton, NJ). A particularly preferred such powder is ANCORSTE
EL 1000C iron powder, which has a particle size of about 13
It has a typical screen profile of about 17% by weight and greater than No. 100 sieve, the balance being between these two dimensions (greater traces than No. 60 sieve). ANCORSTEEL
1000C powder has an apparent density of from about 2.8 to about 3.0 g / cm ^2.

Other iron-based powders useful in the practice of the present invention are ferromagnetic or steel powders that contain an effective amount of an alloying element that is prealloyed with iron.

An example of a good ferromagnetic material is iron particles that are pre-alloyed with small amounts of phosphorus. Other good ferromagnetic materials are mixed with substantially pure iron particles. Ferrophosphor powder, for example an iron-phosphorus alloy or a blend of iron phosphide compounds in powder form. Such a powder mixture is disclosed in U.S. Pat. No. 4,093,449 issued Sep. 1974 to Tengsenius et al.
And U.S. Pat. No. 4,093,449 issued to Svenson et al. In June 1978. Examples of steel powders are iron particles that are pre-alloyed with one or more transition elements or other strengthening elements such as molybdenum, nickel, manganese, copper and chromium. Various prealloyed steel powders that can be used in the practice of the present invention are available from Höganäs as part of their ANCORSTEEL line of steel powders.

The iron-based particles can be first coated with an insulating inorganic material to provide an inner coating underlying the binding polymeric material. Preferably, the inner coating is no more than about 0.2% by weight of the coated particles. Such inner coatings include iron phosphate and soyray, etc. as disclosed in U.S. Patent 5,063,011 issued to Lutz et al.
And alkali metal silicates as disclosed in U.S. Pat. No. 4,601,765 issued July. The disclosures of these patents are incorporated herein by reference.

Any polymeric material that can be sufficiently softened and / or dissolved by a solvent so that it can adhere or bond to the surface of the iron-substrate particles can be used in the present invention. Preferred polymeric materials are thermoplastic materials, especially those having a weight average molecular weight of about 10,000 to 50,000. More preferably, about 175-450 ° F.
It is a thermoplastic polymer having a molecular weight range such that it has a glass transition temperature in the range (about 80-230 ° C.). Examples of thermoplastic materials are polyetherimide, polyethylene ether, polyether sulfone, polycarbonate, polyethylene glycol, polyvinyl acetate and polyvinyl alcohol.

A suitable polycarbonate that can be used as a thermoplastic in the present invention is bisphenol-A-polycarbonate, also known as poly (bisphenol-A-carbonate). These polycarbonates are about 1.2
It has a specific gravity range of ~ 1.6. A specific example is the empirical formula (C ₁₆ H ₁₄
O ₃ ) _n , wherein n is an integer of about 30 to 60, and a poly (oxycarbonyloxy-1,4-phenylene- (1-
Methylethylidene) -1,4-phenylene). Commercially available polycarbonate is LEXAN resin from General Electric. The most preferred LEXAN resins are LEXAN 121 and 141 grades.

Suitable polyphenylene ether thermoplastic resin, (wherein, n about 30 to 100 of an integer) empirical formula (C ₈ H ₈ O) _n a poly (2,6-dimethyl, 1,4-phenylene oxide )
It is. Polyphenylene ether homopolymers are alloying / blending resins such as high impact polystyrenes such as poly (butadiene-styrene); and polyimides.
For example, it can be mixed with nylon 66 as polycaprolactam or poly (hexamethylenediamine-adipate).
These thermoplastic materials have a specific gravity in the range of about 1.0 to 1.4. Commercially available polyethylene is commercially available from General Electric Company as NORYL resin.
The most preferred NORYL resins are NORYL 844,888 and 1222 grades.

A suitable polyetherimide thermoplastic is poly [2,
A 2'-bis (3,4-dicarboxyphenoxy) phenylpropane) -2-phenylene-bis-imide], which is in the empirical formula _{(C 37 H 24 O 6 N} 2) n ( wherein, n is from about 15 to Which is an integer of 27). Polyethylene imide thermoplastic resin is about 1.
It has a specific gravity in the range of 2 to 1.6. Commercially available polyetherimides are available from General Electric under UL
It is commercially available as TEM resin. The most preferred ULTEM resin is ULTEM 1000 grade.

Suitable polyethersulfone thermoplastics have the empirical formula (C
₁₂ H ₁₆ SO _{3) n} (wherein, n has about 50 to 200 of an integer). An example of a suitable commercially available polyethersulfone is commercially available from ICI as VICTREX PES.
The most preferred of these resins is VICTREX PES 52
It is 00 grade.

The polymeric material for use in the present invention is generally provided in the form of particles, which are preferably spherical, but may be, for example, lens-shaped or flake-shaped. The particles are preferably fine enough to pass a No. 60 sieve, US series (about 250 microns or less), and more preferably a No. 100 sieve (about 150 microns or less) And most preferably fine enough to pass through a No. 140 sieve (about 105 microns or less). The absolute diameter of the polymer particles, however,
It is less important than the size of the base particles relative to their size; it is generally preferred that the polymer particles are finer than the iron-base particles. The amount of polymer is generally from about 0.001 to 15% by weight of the combined weight of iron-based particles and polymer particles. Preferably, the polymer is at least 0.2% by weight of the combination and up to about 5% by weight. More preferably, the polymer is about 0.4-2% by weight of the total weight of iron-based particles and polymeric material, and most preferably about 0.6-1.0% by weight.

The iron-based particles and the polymeric particles are mixed together in a dry form, preferably by conventional mixing techniques, to form a substantially homogeneous particle blend. The dry mixture is then contacted with a sufficient solvent to wet the particles and more particularly to soften and / or partially dissolve the surface of the polymer particles, to make them sticky and adhere to the surface of the iron-based particles Or combined. Preferably, the solvent is applied to the dry mixture by sprinkling fine droplets of the solvent during mixing of the dry blend. Most preferably, mixing is continued during the dissolution application to ensure wettability of the polymeric material and homogeneity of the final mixture. Thereafter, the solvent is optionally removed by heating, forced ventilation or vacuum. Mixing can be continued during the solvent removal step, which will help the solvent evaporate. Initial dry blending of the particles and application and removal of the solvent can be carried out in a conventional mixing apparatus provided with appropriate solvent application and recovery means. A conical screw mixer available from Nauta can be used for this purpose.

Organic solvents for the polymeric material can be used. Preferred are methylene chloride, 1,1,2-trichloroethane and acetone. Blends of these solvents can also be used. Preferred combinations for use in the present invention are
Polyetherimide thermoplastic resin is used as the polymer material, and methylene chloride is used as the solvent. The amount of solvent applied to the dry mixture is about 1/100 parts by weight of iron-base powder.
~ 25 parts by weight of solvent. However, it will generally be convenient to calculate the amount of solvent based on the amount of polymeric material present. From these points, about 1.5 to 50 parts by weight, preferably about 3 to 20 parts by weight, per weight unit of the polymer,
More preferably, about 5 to 10 parts by weight of the solvent will wet the mixture well.

The iron / polymer powder composition produced by the method of the present invention can be formed into a magnetic core by a suitable molding technique. In a preferred embodiment, compression molding techniques, wherein the powder composition is charged to a die and heated to a temperature above the glass transition temperature of the thermoplastic, are used to form the magnetic component. Preferably, the die and the composition are heated to a temperature about 25-85 ° C. above the glass transition temperature.
Normal powder metallurgy pressures are applied at the indicated temperatures to pressurize the desired ingredients. A typical compression molding technique is about 5 to 100 tons per square inch (69 to 1379 MPa), preferably about 5 to 100 tons.
A compression pressure in the range of 30-60 tsi (414-828 MPa) is used. Usually up to about 1% by weight of a lubricant can be incorporated into the iron / polymer powder composition, but the lubricant can be applied directly to the die wall. The use of a lubricant reduces the stripping pressure and the sliding pressure. Examples of suitable lubricants are lead stearate or
ACRAWAX is one of the synthetic waxes available from Glycol Chemical Company as a synthetic wax. Another lubricant that can be mixed directly with the iron / polymer powder composition is particulate boron nitride.

Following the compression step, the molding components are optionally heat treated.
By this procedure, the compressed component is preferably removed from the die and allowed to cool to a temperature at least equal to the glass transition of the polymeric material, and then the component is compressed to a `` process '' temperature above the glass transition temperature, preferably. Separately heated to a temperature of up to about 140 ° C. The compressed component is maintained for a process time sufficient for the component to be fully heated and substantially brings its internal temperature to the process temperature. Generally, heating requires about 0.5 to 3 hours, depending on the size of the pressing section and the initial temperature. The heat treatment can be performed in air or in an inert atmosphere such as nitrogen.

Example 1 An iron / thermoplastic powder composition was previously annealed in granular ULTEM 1000 polyetherimide (sieved to remove particles larger than 150 microns) and dissociated ammonia and smaller than about 150 microns and Prepared using substantially pure iron particles sieved to remove particles larger than 375 microns. The iron particles and the thermoplastic particles were mixed by hand in the dry state to obtain an iron / thermoplastic resin composition that was 0.6% by weight of the thermoplastic material. The test composition was prepared by sprinkling methylene chloride over the following amount of the dry mixture while mixing was continued. In the case of a wet mixture, it continued for a further 2-3 minutes after the addition of the solvent was completed to achieve a homogeneous mixture and to assist in removing the solvent by evaporation. After this period, the mixture was sprinkled on trays and dried in air.

Three different test compositions were prepared by the above method using various amounts of methylene chloride as follows: Composition A was 100
Composition B was made with 1.7 parts by weight of solvent per part by weight of iron powder; Composition B was made with 3.3 parts by weight of solvent per 100 parts by weight of iron powder; and Composition C was made with 100 parts by weight of iron powder 8.3 parts by weight of solvent were used. The dry mixture, which had not been treated with the solvent binding technique according to the method of the invention, was kept as a control composition.

Toroids and strength test bars were made from the powder composition to measure magnetic and transverse breaking strength. The material is placed at 525 ° F (about 27 MPa) under 40 tsi (about 552 MPa) pressure.
(4 ° C.) in a die. After compression, the pressurized article was heat treated in air at a temperature of 600 ° F (about 316 ° C) for 1 hour. Transverse rupture strength was measured on heat treated test bars according to ASTM B528-76. The results are shown in Table 1A. As can be seen, the part strength increased at higher solvent levels.

AC iron loss (watts / lb; measured at 500 Hz, 1 Tesla) was measured on the heat treated toroid. The results are shown in Table 1B. Toroids made from the control (no solvent binding) composition exhibited the highest core loss, indicating that the use of solvent demonstrated improvement over simple mixtures.

Example 2 An iron / thermoplastic powder composition was prepared using granular ULTEM 1000 polyetherimide (sieved to remove particles larger than 104 microns) and ANCORSTEEL 1000C iron powder. Iron particles (297.75 pounds) and thermoplastic particles (2.
25 pounds) was mixed in a Nauta conical screw mixer for 15 minutes. Methylene chloride (15 pounds) was added to the mixture over 15 minutes while mixing continued. Mixing of the moistened mixture was continued for another 10 minutes. Thereafter, the solvent was removed by subjecting the mixing vessel to a vacuum, and mixing was continued during this time. The obtained dry powder was discharged from the mixing vessel.

Strength test bars and toroids were made and tested as in Example 1. The results were compared to the same control sample used in Example 1. Table 2 shows the results.

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Claims (17)

(57) [Claims] 1. A method for producing an iron / polymer powder composition of iron-base powder particles bonded to a polymer material, comprising: (a) drying a mixture of iron-base powder particles and polymer material particles; Forming, the polymer comprises about 0.001-5.0% by weight of the mixture; (b) wetting the dry mixture with a solvent for the polymeric material;
Then (c) removing the solvent. 2. The method according to claim 1, wherein the polymeric material is a thermoplastic polymer and the iron-based powder particles are substantially pure iron. 3. The method of claim 2, wherein the polymeric material is a thermoplastic having a weight average molecular weight of about 10,000 to 50,000.
The method described in the section. 4. The thermoplastic material has a glass transition temperature in the range of about 80-230 ° C. and about 0.2-5.0% by weight of the mixture.
3. The method according to claim 2, comprising: 5. The method according to claim 2, wherein the thermoplastic material is a polyetherimide, polyphenylene ether, polyethersulfone or polycarbonate. 6. The method of claim 1, wherein the wetting step includes spraying a solvent over the mixture;
During this time the mixture is further mixed, where the iron particles are about 50
The method of claim 1 having a weight average particle size of up to 0 microns and wherein the particles of polymeric material are finer than about 250 microns. 7. The method of claim 1, wherein the wetting step includes spraying a solvent over the mixture.
6. The method of claim 5, wherein the mixture is further mixed during this time, wherein the solvent is methylene chloride. 8. The method of claim 5, wherein the iron particles have a weight average particle size of up to about 500 microns and wherein the polymeric material is finer than about 250 microns. 9. The method according to claim 5, wherein the polymer comprises about 0.4 to 2% by weight of the dry mixture. 10. The method according to claim 8, wherein the polymer comprises about 0.4 to 2% by weight of the dry mixture. 11. An iron / polymer powder composition formed by the method of claim 1. 12. An iron / polymer powder composition formed by the method of claim 2. 13. An iron / polymer powder composition formed by the method of claim 5. 14. An iron / polymer powder composition formed by the method of claim 7. 15. An iron / polymer powder composition formed by the method of claim 8. 16. An iron / polymer powder composition formed by the method of claim 9. 17. An iron / polymer powder composition formed by the method of claim 10.